Field of the Invention
The disclosed embodiments generally relate to a process for recycling byproducts from a unique gas to liquids process, including wax, light hydrocarbons and syngas, to improve production efficiencies and enable utilization of the technology at a scale smaller than has been previously practiced in industry. More specifically, the disclosed embodiments relate to processes by which catalytic processing may convert natural gas, natural gas liquids, or other hydrocarbon feedstocks into economically valuable hydrocarbon products more efficiently than traditional gas to liquids, or GTL, techniques.
The best known GTL technique is the Fischer-Tropsch (F-T) catalytic process which has developed significantly since the original inventors filed their patents in the 1920's. Today, several large F-T processing plants are in production throughout the world, converting natural gas, coal and other fossil feedstocks into more valuable hydrocarbon products. These plants include Sasol 1 (Sasolburg, South Africa), Sasol Synfuels East & West (Secunda, South Africa), PetroSA (Mossel Bay, South Africa), Shell Middle Distillate Synthesis (Bintulu, Malayasia) and Oryx GTL (Ras Laffan, Qatar). Each of these plants employs different technologies, in many cases with substantial differences. However, one commonality of these plants is that their component technologies make them uneconomical for smaller, more distributed operation. As the investment required for these traditional F-T processing plants costs billions of dollars per installation, these traditional technologies are not economically viable for the deployment of distributed plants. Many billions of dollars worth of natural gas and related products are currently flared or otherwise remain stranded at gas production fields and shale oil operations around the world for lack of appropriate means to convert those hydrocarbons on-site into market viable products.
As global populations continue to develop economically and the demand for energy increases, there will be an ever greater need for new supplies of refined hydrocarbons fuels. In particular, the demand for clean, low sulfur-content, high lubricity, high cetane diesel fuel will increase. While traditional F-T processing will help fill some of the demand, the high up-front investment required by such plants means that they will only be constructed in areas where there are significant quantities of feedstocks that are either freely available or have negative market value (i.e., there is a market value to discarding the feedstocks). A substantial increase in the efficiency and effectiveness of gas to liquids processing at smaller scale can unlock vast stockpiles of energy for world markets.
Related Art
It is known in the art that natural gas or other feedstocks (e.g., natural gas liquids, waste CO2, biomass, associated stranded or flared gas and combinations thereof) can be converted into syngas (herein defined as a mixture comprising primarily hydrogen and carbon monoxide with smaller quantities of other products, including methane, carbon dioxide, argon and nitrogen) by a variety of known thermochemical conversion methods. These methods include partial oxidation, auto-thermal reforming, steam methane reforming, gasification, thy reforming and other known methods. As this is an active area for research and development, technologies for syngas production systems from other carbonaceous resources are also widely known and emerging processes are under development.
The catalytic hydrogenation of carbon monoxide to produce light gases, liquids and waxes, ranging from methane to heavy hydrocarbons (C100 or higher) in addition to oxygenated hydrocarbons is typically referred to as Fischer-Tropsch (F-T) synthesis. Traditional F-T processes primarily produce a wax (C25 to C100 or greater) from a catalytic conversion process. This wax is then hydrocracked and/or further processed to produce diesel fuel, naphtha and other fractions. During the hydrocracking process, light hydrocarbons are also produced, which may require additional upgrading to produce viable products. Some of these processes are known and described in the art.
For example, US Patent Application Publication US2013/0065974 A1, filed Sep. 8, 2011, describes a process in which naphtha is recycled as a feedstock to a syngas generator in a Fischer-Tropsch process.
U.S. Pat. No. 6,262,131 81 (Syntroleum), issued Jul. 17, 2001, describes a structured Fischer-Tropsch catalyst system and method to primarily produce heavy hydrocarbons (C25+) that includes at least one structure having a catalytic surface, such catalytic surface having a linear dimension exceeding 20 mm, a void ratio exceeding 0.6, and a contour that causes non-Taylor flow when CO and H2 pass through the structure. F-T catalysts, including iron and cobalt, are described in the patent.
U.S. Pat. No. 7,404,936 (Velocys, Inc.) issued Jul. 29, 2008, describes a micro-channel reactor system and catalysts used in the micro-channel reactor system to produce heavy hydrocarbons from a syngas steam.
U.S. Pat. No. 4,499,209 (Shell Oil Company), issued Feb. 12, 1985, describes a Fischer-Tropsch catalyst prepared by impregnation of a silica carrier with a solution of zirconium and titanium, followed by calcination and other preparation steps.
U.S. Pat. No. 5,620,670 (Rentech, Inc.), issued Apr. 15, 1997, describes a catalytic process for converting hydrogen and carbon monoxide to heavy hydrocarbons (waxes) in a Fischer-Tropsch synthesis reactor using a promoted iron oxide catalyst slurry.
All of the aforementioned processes produce primarily a hydrocarbon wax that requires processing to create economically viable products. These techniques, such as hydrocracking and other upgrading means, add significant expense and complexity to a plant design. Such relatively expensive processes can be justified for large implementations such as the traditional gas to liquid installations listed above. However, for smaller, distributed plants that require lower volume of feedstock for gas-to-liquids (GTL) synthesis and other plants that produce less than approximately 25,000 barrels per day, traditional F-T plant designs that incorporate hydrocracking and other expensive upgrading processes are generally not economically viable. Any means by which such smaller, distributed plants might be constructed might substantially improve energy production worldwide.